1 //用拉格朗日插值多项式求函数的近似值
2 #include<iostream>
3 using namespace std;
4 void main()
5 {
6 int n,i;
7 float xx,yy;
8 float *x,*y;
9 cout<<"请输入数据表的数据组数：";
10 cin>>n;
11 x=new float[n];
12 y=new float[n];
13
14 cout<<"请依次输入X的值：";
15 for(i=0;i<n;i++)
16 cin>>*(x+i);
17
18 cout<<"请依次输入y的值：";
19 for(i=0;i<n;i++)
20 cin>>*(y+i);
21
22 cout<<"请输入所要计算的X的值：";
23 cin>>xx;
24
25 float Lagrange(float*,float*,float xx, int n);
26 yy=Lagrange(x,y,xx,n);
27 cout<<"当x="<<xx<<"时,"<<"y="<<yy<<endl;
28 }
29
30 float Lagrange(float*x,float*y,float xx,int n)
31 {
32 int i,j;
33 float *a,yy=0;
34 a=new float[n];
35 for(i=0;i<=n-1;i++)
36 {
37 *(a+i)=*(y+i);
38 for(j=0;j<=n;j++)
39 if(j!=i) *(a+i)*=(xx-x[j])/(x[i]-x[j]);
40 yy+=*(a+i);
41 }
42 delete a;
43 return yy;
44 }
